Valorization of Rice Husk Ash (RHA) as silica precursor...

Valorization of Rice Husk Ash (RHA) assilica precursor for the obtainment of clay

bricks and deflocculating additives

Fernanda Andreola, L. Barbieri, I. Lancellotti

Department of Engineering “Enzo Ferrari”

University of Modena and Reggio Emilia, Italy

5th International Conference on Sustainable Solid Waste Management, 21-24 June 2017 - Athens, Greece

ATHENS2017


AIM

Valorize RHA in ceramic field taking advantage ofits feature as amorphous silica source

Obtain ceramic bricks by substitution of clayedmaterials with different percentages of RHA,following the typical brickmaking process

Study an environmental friendly route tosynthesize (from the rice husk ash) sodiumsilicate solutions and check their deflocculantcapability for ceramic bodies.


Burnt outLHV: 15 MJ/kg

Worldwide rice production: 717 million tons/year (Italy: 1.50 million tons/year)

Total global RHA amount : ≈35 million tons/year

Rice husk Rice husk ash (RHA)

UTILIZED AS BIOMASS FUEL: in the rice Parboiling process, cement and brick kilns

IT IS NOT A WASTE: sold and used as a pozzolanic, insulating, waterproofing

and fertilizer material

WHY USE RHA?

22% from milled paddy 25% is generated


RHA CHARACTERIZATION

Rietveld‐R.I.R.Quantitative analysis

Agreement AgreementAgreement indices

Cristobalite 11,5% Rwp = 6,33

Rp = 4,51

χ2 = 5,82Tridymite 2,8%

Amorphous silica 85,7%

SEM microstructureRietveld-RIR analysis

Position [°2Theta]

10 20 30 40 50 60 70

0

100

400

900

1600

RHATQ.RD

C,T

C C

Crystobalite

Trydimite

N C H S

0.18% 9.95% 0.47% 0.48%

Elemental analysis

Bondioli F., Andreola, F., Barbieri, L., Manfredini, T., Ferrari, A.M.:Effect of Rice Husk Ash (RHA) in the Synthesis of (Pr,Zr)SiO4 Ceramic Pigment, J. Euro. Ceram. Soc., 27, 3483-3488 (2007)

5

CURRENT INDUSTRIAL PROCESSES• MELTING PROCESS (OR VETRIFICATION) WITH DISSOLUTION:

• Calcination of a mixture of sodium carbonate (Na2CO3) and natural quartz sand (SiO2) in suitable furnaces at 1400-1500 °C, according to the reaction:

Na2CO3 + m SiO2 Na2O mSiO2 + CO2 Formation of anhydrous sodium silicate (Na2OmSiO2) in molten state (magma).

• Dissolution of the "solid glass" obtained in the previous step, in water, in special autoclaves under high pressure and temperature, according to the reaction:Na2O mSiO2 + n H2O Na2O.SiO2 n H2O + SiO2

• HYDROTHERMAL PROCESSBased on the reaction of silica with a caustic soda solution in autoclave under high pressure and temperature conditions, according to the reaction:

2NaOH + m SiO2 + (n -1 ) H2O Na2O mSiO2 nH2O


6

Slz. NaOH1M, 1.5M, 2M, 3M

Alkaline attack in hermetic teflon vessel using thermostatic bath

SOLID/LIQUID RATIO 1:5

OPERATIVE CONDITIONS

•Molar concent. NaOH(aq):1‐3 M

•Contact time: 1,3,5 hs

•T=80°C; P=1 atm.

•Particle size : <180 , <63 m

Separation of soluble silicates by Filtration

Filter Whatman n° 54 + 52

Ground to improve reactivity

EXPERIMENTAL PROCEDURE

RHA

5th International Conference on Sustainable Solid Waste Management,21-24 June 2017 - Athens, Greece

Ramman

Tritation by HCl 1M

Deflocculating capability tests by

Rotational Reometry

XRD

SEM/EDS

Separation of soluble silicates by Filtration

Filter Whatman n° 54 + 52

CARACTERIZATION NA-SIL SOLUTIONSRaman Spectroscopy

cm⁻¹

Inte

nsità

(arb

itrar

y un

it)

cm⁻¹ λ caracteristic of Si‐O(Na)molecolar lattice

Raman confirmed that the

synthetized Slz are Na‐silicates

Slz.obtained from synthesis

RHA

Commercial Products

SiO2/Na2O = 1:2SiO2/Na2O = 1:1

D. Fortnum and JO. Edwards, J. lnorg. NucI. Chem. 2 (1956) 264.

J.E. Earley, D. Fortnum, A. Wojcicki and JO. Edwards, J. of Am. Chem. Soc. 81 (1959) 1295.



SOLUBLE NA-SILICATES SOLUTION

High reactivity of ash , different ponderal ratio as a function of molar [NaOH] used

Determination SiO2% and Na2O% by titriation method(HCl 1M, methyl red as indicator) based on ISO 2124-1972

1M 1,5M 2M 3M

3.05

2.64

2.241.64

00.5

11.5

22.5

33.5

[NaOH]

Rp (SiO2/Na2O)

after 3 hs

<63 m


Commercial Silicates. Clay 65wt%

The best commercial deflocculant Na-SIL 2:1, the optimum amount is 0.5 wt%

DEFLOCCULANT CAPABILITY


The rheological measures conducted using the same amount ofthe commercial and synthesized solutions (0.5%) highlightedthat all of synthesized solutions have a better performancerespect to the commercial one.

050

100150200250300350400450500

CommercialNa‐SIL. 2:1

Silicatefrom RHANaOH1M

Silicatefrom RHANaOH 1.5M

Silicatefrom RHANaOH 2M

η [m

Pa s]

shear rate 30s‐1

shear rate 200s‐

DEFLOCCULANT CAPABILITY

BRICKMAKING PROCESSRHA (5-20 wt%)

Italian production:

5.2 million ton/y Font: Report ANDIL (2015)


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ExperimentalRaw materials:

Clay mixture /rice husk ash (5-20 wt%)

Mixing Paste(20-27%moisture)

Wet Extrusion

(P=8-9 bar)

Drying (Troom=3hs; 100°C,48 hs)

Firing ind.cycle(960°C,24 hours with 6

hours of soaking temperature)

L.Srinkage, Naphta Absorption, carbonates,

Loss Weigth

L.Srinkage, Water Absorption (24 h), Flexural Strength,

Loss Weigth

SEM, XRD


BRICKS CHARACTERIZATIONAfter drying After firing

2.22

2.95

2.382.19

2.65

0

0.5

1

1.5

2

2.5

3

3.5

0 5 10 15 20 RHA (wt%)

Lin

ear

Sri

nka

ge

(%)

12.06

14.6915.66

18.57

9.68

0

5

10

15

20

25

0 5 10 15 20

RHA (wt%)

N.A

(%

)

RHA (wt%) WA% LS%

0 17.00 0.02

5 19.58 0.06

10 23.00 0.05

15 26.42 0.04

20 32.05 0.04


This image cannot currently be displayed.

5%

20%

SEM/XRD ANALYSIS

10%

0%

Q: SiO2; Ak: Ca2MgSi2O7; G: Ca 2 Al(AlSi)O 7

CONCLUSIONS RHA acts as raw material for brick products due to a high silica

content which have mainly plasticity reducing effect on the brickbodies. Contributes to reduce the linear shrinkage during dryingand firing steps.

With substitutions up to 5 wt% into the bricks bodies, the mainproperties tested are in accordance to the recommended valuesfor roofing bricks. Upper amounts of RHA contributes to increasefinal porosity lightweight bricks

The tests conducted using an environmental friendly route permitto obtain solutions with ponderal ratio SiO2/Na2O 2:1 typical ofcommercial silicates used in ceramic industry as deflocculants.

Rheological measures confirmed that the silicate solutions obtainedare suitable to use as defloculanting additives and showed a betterperformance respect to commercial ones.


THANK YOU FOR YOUR ATTENTION !!!

[email protected]

165th International Conference on Sustainable Solid Waste Management,

21-24 June 2017 - Athens, Greece

The authors acknowledge Eng. Nicole Bagnoli and Eng. E. Guidetti for the thesis projects


Caracterization of ashes after treatmentX-Ray Diffraction

0 20 40 60 80

Arbitrary Unit

2θ

Ceneretq

TQ

1M

4M

It is verified that the alkaline treatment attacks amorphous silica and alsocristobalite crystalline phase decreases intensity.

3 hs 5 hs

<63 μm <180 μm <63 μm <180 μm

% Si % C % Si % C % Si % C % Si % C

RHA tq 41.4 16.0 41.4 16.0 41.4 16.0 41.4 16.0

1 M 30.7 30.0 38.3 30.3 36.3 29.1 38.9 31.7

2 M 31.5 40.0 36.6 44.5 31.0 44.0 32.4 35.1

4M**(1 h) 23.2 52.6 29.6 61.6

Caracterization of ashes after treatmentSEM/EDS

• Using EDS is observed a decrease ofthe Si content after alkaline attack

• The reactivity is high using fine ash• It is not necessary increases to 5 hs

the contact time



OXIDE (wt%) YELLOW CLAY GREY CLAY

SiO2 52,67 50,41Al2O3 11,02 12,16TiO2 0,58 0,61Fe2O3 4,30 4,32CaO 11,96 11,96MgO 2,44 3,12K2O 2,44 3,12Na2O 0,54 0,72ZnO - -PO4 - -SO4 - -MnO - -

L.O.I (1100°C) 13,06 13,77CaCO3 (CALCIMETRY) 18,5 19,5

YELLOW CLAY Illite-mica, Smectite, Kaolinite and Chlorite (traces) , Quartz, K-Feldspars, Carbonate ( calcite and dolomite)

GREY CLAY Illite-mica, Smectite, Kaolinite and Chlorite (traces) , Quartz, K-Feldspars, Carbonate, Hematite in tracce

CLAYS CHARACTERIZATION

LE SOSPENSIONI DEVONO PRESENTARE DETERMINATE

CARATTERISTICHE:

BUONA CAPACITA’ DI SCORRIMENTO

BASSA PERCENTUALE DI ACQUA

AGGIUNTA DI UN DEFLOCCULANTE

AZIONE DISPERDENTE

AZIONE FLUIDIFICANTE

PRINCIPALI MECCANISMI DI AZIONE DEI DEFLOCCULANTI

•Spostamento del pH verso valori basici con immissione di OH-•Sostituzione con cationi alcalini degli altri cationi presenti nel doppio strato;•Aumento della carica negativa delle micelle per adsorbimento di alcuni anioni (TPF, PPA;)•Aggiunta di un colloide protettore che sottrae le particelle all’azione di ioni flocculanti (SIL);

Na2O. nSiO2+H2O nSiO2 +2Na++OH-

Valorization of Rice Husk Ash (RHA) as silica precursor...

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